The present invention relates to a fixed material transportation apparatus transporting a fixed material and a liquid fixing apparatus.
Up to now, there is a construction transporting a sheet, for example, being one of the fixed material, to a recording portion by a sheet transportation apparatus and transporting outside while recording in an ink jet printer, for example, being one of apparatuses for fixing liquid. FIG. 9A is a view showing only the main portion of the sheet transportation apparatus in such the ink jet printer. In such the ink jet printer, recording is performed by a recording head 3 while transporting a sheet 1 sandwiching with a delivery roller 2 and a driven roller thereof 2a, and the sheet 1 is transported to discharge by sandwiching with a discharging roller 4 and a rowel spur 4a as a driven roller.
In the ink jet printer providing the above prior sheet transportation apparatus, the sheet 1 sucks large quantity of ink and rises in wave shape to the recording head 3 side, that is, so-called cockling possibly generates as shown in FIG. 9B at the case that picture to which many ink drops are discharged such as solid picture for example is recorded on the sheet 1. When the cockling generates and grows, a gap between the sheet 1 and the recording head 3 becomes uneven, recording unevenness generate by dispersion of flying distance of the ink drops, or there is a fault that the sheet gets dirty by contacting the recording head 3.
These drawbacks can be prevented by depressing the above cockling in allowance if the span between the delivery roller 2 and the discharging roller 4 is comparatively short. However, it is necessary in near future to increase number of nozzles of every nozzle of each color or to arrange nozzle lines of plural colors to transportation direction of the sheet 1 to make recording speed further high in the ink jet printer and the like. In these cases, dimension of the recording head 3 becomes long to transportation direction of the sheet 1 as shown in FIG. 9C.
When the recording head 3 is long, span between the delivery roller 2 and the discharging roller 4 becomes long so as not to prevent absolutely the cockling in the construction transporting and discharging by sandwiching with the delivery roller 2 and the driven roller 2a, and the discharging roller 4 and rowel spur 4a as the driven roller thereof. Then cockling goes over allowance, and it is considerable that the construction transporting and discharging by sandwiching with such the two pairs of rollers itself is not realized depending on the ink jet printer having long head length.
Such the cockling is comparatively small at using exclusive sheet for ink jet printer as the sheet 1, and is large at using normal sheet. Because of that, paper gap (gap A between the sheet 1 and the recording head 3 in FIG. 9A) is set large considering rise of the sheet caused by cockling at using the normal sheet in the design of ink jet printer and the like. However, when the paper gap is large like this, ink particles discharged from the nozzle of the recording head generate flying curve and dispersion of point of impact becomes large for the flying curve so as to prevent possibly improvement of recording quality.
On the other hand, various kinds of printers having mainly a sucking portion of hollow box shape at transportation surface of the sheet and sucking the sheet through plural penetrating sucking holes provided at the sucking portion by a sucking pump and the like are proposed in recent yeas (see Japanese Unexamined Patent Publications JP-A-63-303781, JP-A-3-270, etc.). Among them, there is a printer proposed that the sheet is sucked to a platen and the like through these sucking holes.
However, only through holes are opened to suck at the sucking portion of the hollow box shape in both of them, and it is difficult to prevent the above cockling over whole surface of the sheet in the recording portion. Further, since the related art described in the above official gazette has the construction that only through holes are opened to suck at the sucking portion of the hollow box shape, strong sucking force possibly causes fall of transportation accuracy. Because of that, in the present circumstances, a printer is not made practicable except a part of large-sized printer performing transportation (using its own weight of the sheet for transportation) to gravity direction as the actual situation.